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Related Experiment Videos

An upper arm model for simulated weightlessness.

A C Parcell1, S W Trappe, M P Godard

  • 1Human Performance Laboratory, Ball State University, Muncie, Indiana, USA.

Acta Physiologica Scandinavica
|April 12, 2000
PubMed
Summary
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Four weeks of arm unloading significantly reduced triceps brachii muscle strength and cross-sectional area. This study suggests arm unloading effectively simulates weightlessness effects on upper limb muscles.

Area of Science:

  • Physiology
  • Muscle Biology
  • Biomechanics

Background:

  • Skeletal muscle adaptations to unloading, such as weightlessness, are a significant concern for astronauts.
  • Understanding muscle response to unloading is crucial for developing countermeasures.
  • Previous research has explored various unloading models, but direct analogues for upper limb muscle changes are still being investigated.

Purpose of the Study:

  • To investigate the functional and structural effects of a 4-week non-dominant arm unloading protocol on the triceps brachii muscle.
  • To determine if arm unloading serves as an effective analogue for simulating weightlessness-induced muscle changes in the upper limb.

Main Methods:

  • Six healthy college-age males underwent 4 weeks of unilateral arm unloading using a sling worn during waking hours.
Keywords:
Non-programmatic

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  • Maximal isometric torque, force-velocity characteristics, and integrated electromyography (IEMG) of the triceps brachii were assessed before and after unloading.
  • Muscle cross-sectional area (CSA) and myosin heavy chain (MHC) isoform composition were analyzed via histochemistry and electrophoresis.

    • Main Results:

    • A significant decline of 12% in maximal isometric torque production and a 4% reduction in upper arm CSA were observed post-unloading (P < 0.05).
    • Integrated electromyography (IEMG) amplitude decreased by 21% during maximal isometric contractions (P < 0.05).
    • A significant increase in myosin heavy chain (MHC) type II isoforms (from 40% to 58%) was noted, while type I MHC showed a non-significant reduction (P < 0.08).

    Conclusions:

    • Four weeks of arm unloading induces significant functional and structural adaptations in the triceps brachii muscle.
    • The observed changes in muscle strength, size, and myosin isoform composition are comparable to those reported in studies of real and simulated weightlessness.
    • Arm unloading presents a viable model for simulating microgravity's effects on human upper limb skeletal muscle, aiding in the development of countermeasures.